Polymethacrylic acid-b-polyalkylene oxide copolymers are known. However, their preparation presents considerable problems. From the prior art, which is not very comprehensive, mention may be made of: J. Polym. Sci. Part A 30, 2251-2261, 1992, describes AB (BA), ABA and BAB block copolymers based on polyethylene oxide and polymethacrylic acid. These products are prepared via a precursor route by first preparing a poly-t-butyl methacrylate-b-polyethylene oxide copolymer or a polyethylene oxide-b-poly-t-butyl methacrylate copolymer by sequential, anionic polymerization of t-butyl methacrylate and ethylene oxide or, conversely, ethylene oxide and t-butyl methacrylate, then subjecting this copolymer to an acid-catalyzed elimination of isobutene from the poly-t-butyl methacrylate segment to give the desired polyethylene oxide-b-polymethacrylic acid copolymers. However, this procedure can hardly be carried out in industry since ionic polymerization requires very pure, water-free solvents (in particular tetrahydrofuran) and reactants. In addition, the reaction has to be carried out at low temperatures of about -78.degree. C. Moreover, the use of specific alkali metal initiators (potassium naphthalide or diphenylmethylpotassium) is necessary.
Similarly, in Eur. Polym. J. 27, 673-680, 1991, Ulbricht et al. describe the preparation of poly-t-butyl methacrylate-b-polyethylene oxide or polyethylene oxide-b-poly-t-butyl methacrylate diblock copolymers by means of anionic polymerization. The authors refer to secondary reactions: inter alia, the use of cumylpotassium as initiator for the polymerization of t-butyl methacrylate at a reaction temperature of 25.degree. C. leads to a series of undesired secondary reactions, recognizable by a broadening of the molecular weight distribution and nonquantitative monomer conversions.
In Macromolecules 15, 223-227, 1982, the synthesis of poly-t-butyl methacrylate-b-polyethylene oxide-b-poly-t-butyl methacrylate copolymers (ABA type) is reported. As initiators, use is made of lithiated diesters of polyethylene oxide. This process too requires extremely high purity of the reagents used and relatively low polymerization temperatures (from -25 to 0.degree. C.). The products obtained have a very broad molecular weight distribution which in this case too points to the occurrence of undesired secondary reactions.
The present invention addresses the industrial problem of preparing block copolymers whose segments are formed from alkylene oxides and methacrylhc acid or its salts. The desired block copolymers should be obtainable in a very simple manner, free of secondary reactions and in high yield in order to make industrial manufacture of these compounds possible.